The present invention relates to a positive-working colored photosensitive recording material for the production of a color test image, composed of a temporary layer carrier, a photosensitive layer containing dyestuff or pigment, binder and quinonediazide compound and an adhesive layer which can be activated by means of heat, and to a process for the production of a color test image using this material.
Color testing is in general performed in multicolor printing to allow correction of the color separations used for exposure of printing plates. The color test image must be a true record of the required dot or line image and should reproduce the tone value of the colors in a form true to nature, i.e. in neither an increased nor reduced form. Visual color testing should indicate defects in the master, allow the best color reproduction to be expected by machine printing, reproduce the accurate gradation of all color shades and indicate whether the gray shades are neutral. It should furthermore indicate any need to attenuate one of the colors and/or give an indication to change the film master before production of the printing plates.
Color testing for multicolor printing has to date been carried out with the aid of color proofs. All the steps which are also needed for the actual multicolor printing must be taken in this process. Such a color test process is expensive and time consuming, and other color test processes have therefore been developed, which are intended to be of equivalent quality to the proof. Three color test processes using photosensitive color test films are known, the surprint process (laminating on top of one another), the surlay process (copying on top of one another), and the overlay process (laying on top of one another).
DE-A 2,712,864, corresponding to GB-A 1,550,524, describes a positive-working color film which consists of a transparent layer carrier, a layer containing a photosensitive diazonium salt and a thin color layer containing a dispersed pigment. A specific layer arrangement is characteristic of this color test film, and the layer containing the photosensitive diazonium compound should in all cases be above the color layer with respect to the exposure stage.
EP-A 0,035,028, corresponding to U.S. Pat. No. 4,260,673, relates, to a presensitized color test sheet which has the following layer build-up: a carrier sheet is covered with anon-stick coating, onto which a color layer is applied, followed by a novolak-containing binder layer which contains a reaction product of a resin and a diazo oxide and is free from pigments. This binder layer is then also followed by a barrier layer and a non-stick layer.
EP-A 0,217,792 relates to a process for improving the exposure range of positive-working color test films in which a colored release layer is used as an optical filter. A color test film which, in addition to the other layer build-up, also additionally contains one or more dyestuffs which effect protection from reflection ("antihalation layer") is known from EP-A 0,165,030.
EP-A 0,165,031, corresponding to U.S. Pat. No. 4,656,114, discloses a color test sheet in which, between the color layer and the adhesive layer, there is an additional water-insoluble transparent barrier layer which is intended to prevent diffusion from one color layer into another color layer after the adhesive layer has been dissolved.
The primary aim of these known color test processes is to produce a multicolor image which is as close as possible in appearance to the four-color print sought. The decisive disadvantage of these positive-working recording materials for the production of color test films seems to be that these materials use novolak resins in combination with quinonediazide processes as the photoreactive system. Since novolaks have a yellow to brown coloration, this unavoidably leads to a shift in color shade in the color test image to be produced. All the color test systems known to date which are based on precolored layers containing novolak are therefore to be regarded as a compromise between photoreactivity and color reproduction.
In EP-A 0,179,274, corresponding to U.S. Pat. No. 4,659,642, an attempt is made to avoid the color shift due to the intrinsic coloration of the novolak by using binders which are free from phenol groups. However, this does not yet lead to materials which are suitable in practice, since the differentiation between the solubility of the exposed and non-exposed regions is inadequate.
Various processes based on precolored layers are known for the production of color test films for the graphics industry. U.S. Pat. No. 3,671,236 describes a process in which separation images in the various base colors are combined in succession on a receiver sheet in accordance with the corresponding color separations to give a four-color overall image.
U.S. Pat. No. 3,721,557, corresponding to DE-B 1,912,864, describes a process for transferring color images, in which a peel-off layer is applied between the photosensitive layer and the layer carrier. When the photosensitive layer is developed, the soluble constituents of the layer are removed selectively and a visible image forms. The layer carrier with the image is pressed against a suitable receiver material coated with adhesive and the image is then transferred by peeling off the layer carrier. A fresh adhesive layer is applied to the receiver material for each further image transfer.
A color test process in which positive-working photosensitive layers, colored in the desired base colors and in each case on a temporary carrier film, are exposed and developed on this film is known from DE-A 2,236,941, corresponding to U.S. Pat. No. 4,093,464. The resulting separation images are transferred onto an image-receiving material, for example a printing paper, by lamination in register. This process has the disadvantage that lamination in register requires very precise work and is therefore very expensive. Furthermore, lamination of developed images can be carried out only with layers which are still sufficiently thermoplastic, i.e. as a rule only with positive-working layers which additionally also contain certain plasticizing additives.
According to EP-A 0,035,028, a multicolor test image is produced by laminating the multilayered material onto an image-receiving material, which is a paper with a water-proof finish, and exposing it on this material and developing it into the separation image. The other separation images are produced over the first in the same manner. Multicolor images in accurate register can be obtained more easily by this process, since it is merely necessary to perform the exposure in register. The process has the disadvantage that several layers on top of one another are required for each base color and that the image elements still each contain two layers containing non-decomposed colored diazo compound.